Absolutely. The venom would stew from the salivary glands into the broth of the stew. You would definitely become poisoned by eating the parts and drinking the (now-poisonous) broth. It wouldn't take very long, assuming you eat the entire octopus and stew. I would think less than 2 hours, generous, without medical treatment. You would become paralyzed and not be able to call for medical help.
And of course, you would proceed to die.
So stewing a blue ring octopus for dinner should not be high on your list on things to do... unless it's the last thing on your bucket list and have just been DYING to get a taste. ;D